Earlier this week the government was defeated in the Lords on the Crime and Courts Bill.

Before the summer, it had to pull its Lords Reform proposals, when it became clear they would not get through the Commons. Next week, MPs will be debating what, if anything, to do about regulating the press. In the new year, there'll be a bill on gay marriage. And eventually, there may be a Commons vote on cutting the number of MPs from 650 to 600 and redrawing constituency boundaries in the process.

How are all these things related?

The answer is that this week's Lords defeat was the result of an ad-hoc coalition on a particular issue. Labour peers, crossbenchers and Liberal and Conservative rebels combined and found they constituted a majority in the Upper House. The end of Lords reform was the product of Labour siding with a huge backbench Tory rebellion. And if the other matters get through Parliament, it will be because other coalitions have formed behind them; not because a majority government has willed it.

My point is that the days of an imperial majority getting its way in Parliament are, at least for the time being, over.

Take gay marriage - there may be strong opposition (mostly) on the Conservative benches, but there is a clear majority in the Commons (a chunk of Conservative MPs, plus most Labour and Lib Dems) which can be expected to vote a bill through. There may be a similar alignment in favour of press regulation (although the cast of characters may be a bit different, particularly on the Conservative side).

But on parliamentary boundaries, the Conservatives may be able to offer Northern Ireland's DUP, the SNP and the Welsh nationalists sufficient inducements, in the form of extra devolution, to get the proposals through, in the teeth of Labour and Lib Dem opposition. They're certainly making strenuous attempts to pull a majority together.

So the question to ask about any contentious vote in the Commons is not just "will the coalition hold together?" but "which coalition will turn up?" On the central questions of economic policy the Lib-Con coalition has so far managed to command a Commons majority. But on some issues of social policy and matters like press regulation, particularly those which are outside the Coalition Agreement, that majority may not be there, and Lib Dems or, perhaps Tory backbenchers, may go walkabout.

Unofficial whips like Jesse Norman, who engineered the defeat of Lords reform in the Commons, or Mark Reckless, on the EU Budget, have demonstrated that independent-minded MPs can get their way if they have the tactical nous and determination to construct a Commons majority.

Which is why David Cameron may not be able to prevent statutory regulation of the press. It is quite possible to imagine a bill going through on the votes of Labour and Lib Dems and some Tory MPs, and bypassing the Department of Culture Media and Sport.

Government's grip on Parliament has not been this weak for generations.